Polymer welding process and composition

ABSTRACT

A resinous block copolymer, such as butadiene/styrene block copolymer, having an antiblocking agent incorporated therein, such as a microcrystalline wax, is bonded or welded together with a composition containing at least one hydroxyl-ether and/or keto-ether such as 4-methoxy-4-methyl-2-pentanone.

This application is a division of application Ser. No. 770,488, filedAug. 29, 1985, now U.S. Pat. No. 4,666,549.

BACKGROUND OF THE INVENTION

This invention relates to welding polymers. More particularly, thisinvention relates to welding resinous block copolymers containingantiblocking agent.

Solvent welding of thermoplastic resinous polymers has been known forsome time utilizing such solvents as methylene chloride, methyl ethylketone, perchloroethylene, and 1,1-dichloroethane. However, thesesolvents suffer from one or more disadvantages such as toxicity, expenseand the promotion of stress cracking in the welded polymer.

These solvents impose an additional problem when used to bond resinousblock copolymers containing an antiblock agent such as amicrocrystalline wax as disclosed in U.S. Pat. No. 3,766,114, thedisclosure of which is incorporated herein by reference. With this typeof block copolymer that contains an antiblock agent the usual solventmaterials employed for solvent welding cause serious problems becausethe solvent materials dissolve the wax as well as soften or dissolve thepolymer. This dissolved wax tends to remain sticky or tacky for extendedperiods of time at the surface, thus causing difficulties in handlingthe solvent welded articles.

OBJECT OF THE INVENTION

It is an object of this invention to provide a composition and processto weld polymers; it is yet a further object of this invention toprovide a permanently welded resinous block copolymer which has goodblocking characteristics; and it is yet a further object of thisinvention to avoid the deleterious effects on weldability caused byantiblocking agents.

DESCRIPTION OF THE INVENTION

In accordance with this invention a polymer is welded with a compositioncontaining at least one hydoxyl-ether and/or keto-ether.

In accordance with a specific aspect of this invention, a resinous blockcopolymer having an antiblock agent therein is welded with a weldingcomposition containing at least one hydroxyl-ether and/or keto-ether.

In a specific welding process a surface softening amount of at least onehydroxyl-ether and/or keto-ether is applied to at least one surface of aconjugated diene/monovinyl substituted aromatic block copolymer for asufficient length of time to soften the copolymer and then the softenedcopolymer surface is contacted with another surface under conditionssufficient to bond the two surfaces.

DETAILED DESCRIPTION OF THE INVENTION

It is envisioned that any polymer that is compatible with thehydroxyl-ether and/or keto-ether can be welded according to thisinvention. However, the preferred being resinous block copolymers.

The present invention is most useful when welding a resinous blockcopolymer containing a microcrystalline wax antiblock agent.

The resinous block copolymer can be any resinous block copolymer of aconjugated diene and a monovinyl-substituted aromatic compound.

Suitable conjugated dienes or mixtures thereof that can be employedincludes those having 4-12 carbon atoms per molecule, those containing4-8 carbon atoms being preferred. Exemplary of suitable compounds are1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, piperylene,3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, and the like, andmixtures thereof, 1,3-butadiene being particularly preferred.

The monovinyl-substituted aromatic compounds are those containing 8-18carbon atoms per molecule. Examples of suitable compounds includestyrene, 3-methylstyrene, 4-n-propylstyrene, 4-cyclohexylstyrene,4-decylstyrene, 2-ethyl-4-benzylstyrene, 4-p-tolylstyrene,4-(4-phenyl-n-butyl)styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, andthe like, styrene being preferred.

The polymers can be of either an A-B configuration, an A-B-Aconfiguration, or a coupled radial (AB)-(BA)_(n) configuration where nis 2 or more, preferably 2 or 3. The coupling agent is disregarded inthe last formula since it is so small compared with the length of thepolymer chains. This latter formula can also be expressed X(BA)_(n)where X is the coupling agent and n is greater than 2. The A is theresinous monovinyl-substituted aromatic compound block which canoptionally have incorporated therein a small amount of a comonomer. TheB is a rubbery diene block which optionally can have some comonomerincorporated therein, the B blocks being insufficient to cause the totalblock copolymer to be rubbery.

By resinous is meant a normally solid material not having rubberproperties. Generally such materials will have a Shore D hardness (ASTMD2240-75) of greater than about 62, preferably greater than about 69.

The preferred polymers are radial polymers, the preparation of which isbroadly disclosed in Zelinski et al, U.S. Pat. No. 3,281,383 issued Oct.25, 1966, the disclosure of which is hereby incorporated by reference,it being understood that the radial block copolymers of this inventionare limited to those having resinous characteristics. Resinous blockcopolymers having branches of polymer which demonstrate a plurality ofmodes on a gel permeation chromatograph curve prior to coupling aredisclosed in Kitchen et al., U.S. Pat. No. 3,636,517, issued Feb. 1,1972, and Kitchen, U.S. Pat. No. 4,091,053, issued May 23, 1978, thedisclosures of which are hereby incorporated by reference, areespecially preferred.

Briefly the preferred resinous radial block polymers to which thisinvention applies can be prepared by producing a block ofmonovinyl-substituted aromatic compound in the preference of anorganolithium initiator to give a block containing an active lithiumatom on one end of the polymer chain. This living chain is then reactedwith the conjugated diene monomer to give a block copolymer chain withan active lithium atom at one end thereof. This lithium-terminatedcopolymer is then reacted with a compound which has at least threereactive sites capable of reacting with the lithium-carbon bond andadding to the carbon possessing this bond in the polymer. The result isa polymer having relatively long branches which radiate from the nucleusformed by the polyfunctional compound reacted with thelithium-terminated polymer.

The anti-block agent which is present in the polymer can be anyconventional antiblock agent used in the art including microcrystallinewaxes, stearates such as sodium stearate, alkyl amines, stearamides, andthe like. Most preferred are microcrystalline paraffin waxes having amelting point in the range of 180°-200° F. Such materials are sold byBareco Division, Petrolite Corporation. The antiblock agent can bepresent in an amount within the range of about 0.1 to about 20 weightpercent based on the weight of the polymer although generally lowerconcentrations are used particularly where it is desired to have a finalproduct which is clear. Preferred concentrations are in the range of 0.1to 0.5 weight percent based on the weight of block copolymer. Inaccordance with this preferred embodiment samples having a haze of lessthan about 4.5-6 percent preferably less than about 2.5-4 percent (ASTMD1003-61 using Gardner Hazemeter) can be produced, the haze beingdetermined on 100 ml thick injection molded specimens.

The welding composition in addition to at least one keto-ether and/orhydroxyl-ether solvent can also contain a viscosity improving amount ofa polymer. Welding compositions, among other things, have a tendency torun off the surface to be welded. The more viscous welding compositionsescape some handling problems and allow efficient utilization of thesolvent.

Any polymer is considered to be useful to increase the viscosity of thewelding solvent so long as it is compatible with the polymer material tobe welded. When a resinous block copolymer is to be welded, it ispreferred that the viscosity improving polymer be the same resinousblock copolymer, thus avoiding compatibility problems.

The preferred amount of polymer added to the welding solvent is in therange from about 0.5 up to about 10 weight percent in the solvent,preferably from about 1 to about 5 weight percent.

Optionally, various colorants can be added to the welding composition inorder to maintain a color match with the parts that are being bonded inthe solvent welding operation.

Any hydroxyl-ether and/or keto-ether and mixtures thereof are considereduseful for this invention. More particularly hydroxyl-ethers andketo-ether of the formula:

    R.sub.2 C(OR')CR.sub.2 CROHCR.sub.3

    and

    R.sub.2 C(OR')CR.sub.2 COCR.sub.3

respectively, wherein R is hydrogen or an alkyl group having from 1-5carbon atoms wherein each R can be the same or different and wherein R'is an alkyl group having from 1-5 carbon atoms. The most preferredformulas are:

    (CH.sub.3).sub.2 C(OR')CH.sub.2 CHOHCH.sub.3

    and

    (CH.sub.3).sub.2 C(OR')CH.sub.2 COCH.sub.3.

Examples of hydroxyl-ethers include 4-ethoxy-4-methyl-2-pentanol;4-propoxy-4-methyl-2-pentanol; and 2-methoxy-4-hexanol,4-methoxy-4-methyl-2-pentanol being preferred.

The keto-ethers are preferred. Examples of keto-ethers include4-ethoxy-4-methyl-2-pentanone; 4-propoxy-4-methyl-2-pentanone; and2-methoxy-4-hexanone, 4-methoxy-4-methyl-2-pentanone being the mostpreferred.

The compound 4-methoxy-4-methyl-2-pentanone can be made by the reactionof anhydrous methanol with 2-methyl-2-pentene-4-one (commonly known asmesityl oxide) in the presence of a strongly basic ion exchange resin(Belgium Pat. No. 631,124). This compound was available from Shell OilCompany as PENT-O-XONE® solvent.

The polymer part which is to be solvent welded can be treated with thesolvent welding composition according to this invention in conventionalways such as by dipping, application through a porous applicator roller,brushing, or by contact with a syringe type applicator for thoseapplications needing a very thin or narrow solvent welded joint.

The solvent welding composition can be applied at any compatibletemperature so long as the polymer does not melt or the solvent dry toofast. The preferred temperature is that ranging from ambient roomtemperature up to a slightly elevated temperature.

The polymer surface can be treated with the solvent welding compositionfor any length of time sufficient to soften the polymer joint,preferably from at least about 30 seconds up to about 90 seconds.

After application of the solvent welding composition the two parts arejointed by being pressed together under pressure adequate to maintaincontact of the surfaces but not so excessive as to cause significantflow of the softened polymer at the interface of the joint.

EXAMPLE

Two possible welding solvents were tested on K-RO3 (Phillips PetroleumCo.), a resinous butadiene/styrene block copolymer containingmicrocrystalline wax antiblock agent. PENT-O-XONE® (Shell Chemical Co.4-methoxy-4-methyl-2-pentanone) did not dissolve the wax antiblockagent, but did dissolve the copolymer. TETRALIN (Tetrahydro-naphthalene)did dissolve the wax slightly.

PENT-O-XONE® solves the problem present when standard solvents are usedon this copolymer; it does not dissolve the wax, therefore, the wax doesnot interfere with the welding of the copolymer.

TETRALIN does not work as well as PENT-O-XONE® and is very toxic.

As shown by the above example, the instant invention is useful forwelding polymers, particularly useful in welding resinousbutadiene/styrene block copolymers containing a microcrystalline waxantiblock agent. With this type of block copolymer the usual solventmaterials employed for solvent welding cause serious problems becausethey also dissolve the wax as well as softening the polymer. Thisdissolved wax tends to remain sticky or tacky for extended periods oftime at the surface, thus causing difficulty in handling the solventwelded articles. The composition employed, according to the instantinvention, appears to work very well because it does not dissolve thewax antiblock agent and thus avoids the tacky or sticky situation at thesolvent welded joint.

That which is claimed is:
 1. A composition for welding polymerscomprising a welding solvent selected from the group consisting ofhydroxyl-ethers and keto-ethers and a sufficient amount of a resinousconjugated diene/monovinyl-substituted aromatic block copolymercontaining an antiblocking agent, to raise viscosity and lower afterwelding drying time of said solvent.
 2. The composition according toclaim 1 wherein the conjugated diene has 4 to 8 carbon atoms permolecule and the monovinyl-substituted aromatic has 8 to 18 carbon atomsper molecule.
 3. The composition according to claim 2 wherein the blockcopolymer is resinous butadiene/styrene resinous block copolymer.
 4. Thewelding composition according to claim 1, wherein the welding solvent is4-methoxy-4-methyl-2-pentanone.
 5. The composition according to claim 4wherein the block copolymer is resinous butadiene/styrene resinous blockcopolymer.
 6. The composition according to claim 5 wherein the amount ofresinous butadiene/styrene block copolymer in the welding solvent is inthe range of about 0.5 to about 10 weight percent, based on the totalweight of the composition.
 7. The composition according to claim 6wherein the block copolymer in the welding solvent is in the range ofabout 1 to about 5 weight percent.
 8. The composition according to claim1 wherein the welding composition contains a pigment.
 9. The compositionaccording to claim 1 wherein the antiblock agent is a microcrystallinewax.
 10. The composition according to claim 1 wherein the weldingsolvent is 4-methoxy-4-methyl-2-pentanol.
 11. A composition for weldingpolymers comprising a welding solvent and a sufficient amount of aresinous block copolymer containing an antiblocking agent, to raiseviscosity and lower after welding drying time, wherein said weldingsolvent is selected from the group consisting of hydroxyl-ethers andketo-ethers of the formula:

    R.sub.2 C(OR')CR.sub.2 CROHCR.sub.3

    and

    R.sub.2 C(OR')CR.sub.2 COCR.sub.3

respectively, wherein R is hydrogen or an alkyl group having 1-5 carbonatoms wherein each R can be the same or different and wherein R' is analkyl group having 1-5 carbon atoms, and said block copolymer is aresinous conjugated diene/monovinyl-substituted aromatic block copolymercontaining microcrystalline wax antiblock agent.
 12. The weldingcomposition according to claim 11 wherein said hydroxyl-ethers andketo-ethers are of the formula:

    (CH.sub.3).sub.2 C(OR')CH.sub.2 CHOHCH.sub.3

    and

    (CH.sub.3).sub.2 C(OR')CH.sub.2 COCH.sub.3

respectively.
 13. The composition according to claim 11 wherein saidhydroxyl-ethers are selected from the group consisting of4-ethoxy-4-methyl-2-pentanol, 4-propoxy-4-methyl-2-pentanol,2-methoxy-4-hexanol, and 4-methoxy-4-methyl-2-pentanol and saidketo-ethers are selected from the group consisting of4-ethoxy-4-methyl-2-pentanone, 4-propoxy-4-methyl-2-pentanone,2-methoxy-4-hexanone, and 4-methoxy-4-methyl-2-pentanone.
 14. Thecomposition according to claim 11 wherein the conjugated diene ad themonovinyl-substituted aromatic of said resinous conjugateddiene/monovinyl-substituted aromatic block copolymer have 4-8 carbonatoms per molecule and 8-8 carbon atoms per molecule respectively. 15.The composition according to claim 14 wherein said resinous conjugateddiene/monovinyl substituted aromatic block-copolymer is resinousbutadiene/styrene block copolymer.
 16. The composition according toclaim 15 wherein said resinous butadiene/styrene block copolymer in thecomposition is in the range of about 0.5 to about 10 weight percentbased on the total weight of the composition.
 17. The compositionaccording to claim 16 wherein said resinous butadiene/styrene blockcopolymer in the composition is in the range of about 1 to about 5weight percent based on the total weight of the composition.
 18. Thecomposition according to claim 16 wherein said composition contains apigment.
 19. The composition according to claim 16 wherein said weldingsolvent is 4-methoxy-4-methyl-2-pentanone.
 20. A composition for weldingpolymers comprising a welding solvent selected from the group consistingof hydroxyl-ethers and keto-ethers, and having dissolved therein about0.5 to about 10 weight percent, based on the weight of said composition,of a resinous conjugated diene/monovinyl-substituted aromatic compoundblock copolymer.
 21. A composition for welding polymers consistingessentially of a welding solvent selected from the group consisting ofhydroxyl-ethers and keto-ethers, and having dissolved therein about 0.5to about 10 weight percent, based on the weight of said composition, ofa resinous conjugated diene/monovinyl-substituted aromatic blockcopolymer.
 22. A composition according to claim 21 wherein said weldingsolvent is 4-methoxy-4-methyl-2-pentanone, and wherein said resinousconjugated diene/monovinyl-substituted aromatic block is astyrene/butadiene block copolymer which contains microcrystalline waxantiblock agent; and wherein said composition consists essentially of4-methoxy-4-methyl-2-pentanone and having dissolved therein about 0.5 toabout 10 weight percent, based on the weight of said composition, of aresinous styrene/butadiene aromatic block copolymer containing amicrocrystalline wax antiblock agent.